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Sökning: WFRF:(Andreasson Håkan)

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  • Andréasson, Håkan (författare)
  • Pseudomyxoma Peritonei Aspects of Natural History, Learning Curve, Treatment Outcome and Prognostic Factors
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Pseudomyxoma peritonei (PMP) is a rare disease characterized by mucinous peritoneal metastasis (PM). Different loco-regional treatment strategies, i.e. debulking surgery and cytoreductive surgery (CRS) in combination with hyperthermic intraperitoneal chemotherapy (HIPEC), have changed the prognosis for these patients. CRS is an aggressive surgical procedure with a long learning curve. PMP exists in different types; how many depends on which classification is used.The aims of this thesis were to investigate the time-frame of PMP development from an isolated appendiceal neoplasm, examine the learning process for CRS, evaluate the differences in treatment outcome between debulking surgery and CRS in combination with HIPEC, to evaluate a more detailed PMP classification and to investigate particularly interesting new cysteine-histidine (PINCH) protein as a prognostic factor for PMP.Retrospectively 26 PMP patients were identified as having had an appendectomy with a neoplasm in the appendix but with no evidence of PM at the appendectomy. They were treated for PMP within a median of 13.1 months (3.8-95.3) after the appendectomy. No difference was seen between the types of PMP regarding the time to a clinically significant development of PMP and how much tumour was found at treatment. CRS is a highly invasive treatment and stabilization in the learning curve was seen after 220±10 procedures. Patients treated with CRS+HIPEC had a better 5-year overall survival (OS) than patients treated with debulking surgery, 74% vs. 40%. CRS increased the rate of complete cytoreduction from 25% in patients treated with debulking surgery to 72%. The new four-grade PMP classification showed very good inter-rater agreement between two independent pathologists and a difference in survival rates was observed between the different grades. A positive PINCH staining was recorded in 83% of the tumours and that was associated with poorer survival.
  • Andreasson, Håkan, 1966- (författare)
  • Regularity Results for the Spherically Symmetric Einstein-Vlasov System
  • 2010
  • Ingår i: Annales Henri Poincare. - 1424-0637. ; 11:5, s. 781-803
  • Tidskriftsartikel (refereegranskat)abstract
    • The spherically symmetric Einstein-Vlasov system is considered in Schwarzschild coordinates and in maximal-isotropic coordinates. An open problem is the issue of global existence for initial data without size restrictions. The main purpose of the present work is to propose a method of approach for general initial data, which improves the regularity of the terms that need to be estimated compared to previous methods. We prove that global existence holds outside the center in both these coordinate systems. In the Schwarzschild case we improve the bound on the momentum support obtained in Rein et al. (Commun Math Phys 168:467-478, 1995) for compact initial data. The improvement implies that we can admit non-compact data with both ingoing and outgoing matter. This extends one of the results in Andreasson and Rein (Math Proc Camb Phil Soc 149:173-188, 2010). In particular our method avoids the difficult task of treating the pointwise matter terms. Furthermore, we show that singularities never form in Schwarzschild time for ingoing matter as long as 3m
  • Andreasson, Håkan, 1966-, et al. (författare)
  • Rotating, Stationary, Axially Symmetric Spacetimes with Collisionless Matter
  • 2014
  • Ingår i: Communications in Mathematical Physics. - 0010-3616 .- 1432-0916. ; 329:2, s. 787-808
  • Tidskriftsartikel (refereegranskat)abstract
    • The existence of stationary solutions to the Einstein–Vlasov system whichare axially symmetric and have non-zero total angular momentum is shown. This pro-vides mathematical models for rotating, general relativistic and asymptotically flat non-vacuum spacetimes. If angular momentum is allowed to be non-zero, the system ofequations to solve contains one semilinear elliptic equation which is singular on the axisof rotation. This can be handled very efficiently by recasting the equation as one for anaxisymmetric unknown onR5.
  • Andreasson, Håkan, 1966- (författare)
  • Sharp bounds on 2m/r of general spherically symmetric static objects
  • 2008
  • Ingår i: Journal of Differential Equations. - 0022-0396 .- 1090-2732. ; 245:8, s. 2243-2266
  • Tidskriftsartikel (refereegranskat)abstract
    • In 1959 Buchdahl [H.A. Buchdahl, General relativistic fluid spheres, Phys. Rev. 116 (1959) 1027-1034] obtained the inequality 2 M / R ≤ 8 / 9 under the assumptions that the energy density is non-increasing outwards and that the pressure is isotropic. Here M is the ADM mass and R the area radius of the boundary of the static body. The assumptions used to derive the Buchdahl inequality are very restrictive and for instance neither of them hold in a simple soap bubble. In this work we remove both of these assumptions and consider any static solution of the spherically symmetric Einstein equations for which the energy density ρ ≥ 0, and the radial and tangential pressures p ≥ 0 and pT satisfy p + 2 pT ≤ Ω ρ, Ω > 0, and we show thatunder(sup, r > 0) frac(2 m (r), r) ≤ frac((1 + 2 Ω)2 - 1, (1 + 2 Ω)2), where m is the quasi-local mass, so that in particular M = m (R). We also show that the inequality is sharp under these assumptions. Note that when Ω = 1 the original bound by Buchdahl is recovered. The assumptions on the matter model are very general and in particular any model with p ≥ 0 which satisfies the dominant energy condition satisfies the hypotheses with Ω = 3.
  • Andreasson, Håkan, 1966-, et al. (författare)
  • Spherically symmetric steady states of John elastic bodies in general relativity
  • 2014
  • Ingår i: Classical and quantum gravity. - 0264-9381 .- 1361-6382. ; 31:16
  • Tidskriftsartikel (refereegranskat)abstract
    • We study some properties of static spherically symmetric elastic bodies in general relativity using both analytical and numerical tools. The materials considered belong to the class of John elastic materials and reduce to perfect fluids when the rigidity parameter is set to zero. We find numerical support that such elastic bodies exist with different possible shapes (balls, single shells and multiple shells) and that their gravitational redshift can be very large (z approximate to 2.8) without violating the dominant energy condition. Moreover we show that the elastic body has finite radius even in the case when the constitutive equation of the elastic material is a perturbation of a polytropic fluid without finite radius, thereby concluding that such fluids are structurally unstable within the larger class of elastic matter models under study.
  • Andreasson, Håkan, 1966-, et al. (författare)
  • Static solutions to the Einstein-Vlasov system with a nonvanishing cosmological constant
  • 2015
  • Ingår i: SIAM Journal on Mathematical Analysis. - 0036-1410 .- 1095-7111. ; 47:4, s. 2657-2688
  • Tidskriftsartikel (refereegranskat)abstract
    • We construct spherically symmetric static solutions to the Einstein-Vlasov system with nonvanishing cosmological constant Λ. The results are divided as follows. For small Λ > 0 we show the existence of globally regular solutions which coincide with the Schwarzschild-deSitter solution in the exterior of the matter regions. For Λ
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